Haldane commences the article with the statement of obvious — scientists never compare animals based on the size they have. The author provides an example from the story about Jack the Giant Killer, making a point that the bigger are the height and weight, the thicker and stronger bones are required in order to support the living mass like that. Animals of one order have may have similar weight, but absolutely varying body constitution — the weight is distributed in different ways.
Gravity is the factor, affecting animals of big size and weight, but insignificant for the small mammals or insects. They are not afraid of falling from big heights, but the tension of the surface is what makes them suffer. E.g., big mammals have a comparably insignificant amount of water distributed all over their body surface, while small and miniature animals might be carrying their own weight or even a few times their own weight, if bathed in water. Another difficulty, caused by gravity, get tall animals, as they need to have the blood pumped way higher, under high pressure, with stronger vessels.
Miniature size and proportions allow simplicity of the body constitution of the animal, e.g. of a worm. With the increase of weight the size of the body surface increases times less and the proportion cannot be kept. The worm gets enough oxygen from the atmosphere, while humans have lungs, allowing increasing the absorption area tenfold compared to the one, provided by skin. Same goes for the inner organs — they get more complex with the increase in size and weight to provide enough support for the body. Special proportions needs to be kept up while calculating the speed of flight in relation to the length of the aircraft and its weight. Big birds usually have enormous wing span, but their weight remains rather low, and flying is basically soaring on the passing air streams.
The loss of body heat is proportional to the area of skin of the animal; thus, the amount of food, consumed to replenish the energy loss depends on it as well. Author says that “five thousand mice weigh as much as a man”(Haldane n.p.), but there oxygen and food consumption is 7 times higher, same as the heat loss. Author argues that is the cause small animals do not live in the north, small birds move to the south for winter and insects die to revive from their own eggs the next warm season.
Eye works on the principle of proportions as well. It must have enough size for the rods and tubes to reflect the picture of the environment properly and not to distort it. Animals of small size have relatively big eyes compared to their body size to be able to distinguish between the objects, while the big mammals like whales or elephants have the eyes only a bit larger than the humans. People often use the proportions in an odd way, as they “believe that if a flea were as large as a man it could jump a thousand feet into the air”(Haldane n.p.), which is not true since height of the animal’s jump in not proportional to its size, but depends on the energy spent for the jump and considers the weight of the animal.
Haldane agrees with ancient Greek philosophers that the smaller the state the easier it is for the democracy to make the rules of the society. Author finds the beliefs of the socialists about running the country not grounded, and compares to the elephant turning somersaults.
Haldane chose an interesting approach to the traditional layout of the common biology. He made his point, explaining everything with examples and adding a new vision of the animal world of the Earth. He proved fauna can be researched, using alternative approaches. I believe we need to ask him whether the flora can be studied using the same approach, i.e. by size and dimensions?